April 9, 2014
Contact: Shelley Dawicki
NEFSC Researcher Contributes Modeling Skills to Leatherback Sea Turtle Study
A recent study of migrating leatherback turtles on the Northeast U.S. shelf that relied on satellite tagging brought together an interesting group of researchers, among them Northeast Fisheries Science Center (NEFSC)’s Tim Miller, a co-author of the study published March 19 in PLOS ONE. The study, conducted between 2007 and 2010, monitored the movements and diving patterns of 20 leatherbacks in different regions of the Northwest Atlantic, and was one of just three worldwide to study adult males and subadults in habitats where they forage for food.
Although Miller is a biologist, he is not a turtle researcher. He works in NOAA’s Fisheries and the Environment (FATE) program at the NEFSC’s Woods Hole Laboratory, where he uses his statistical and analytical skills and knowledge of marine species to incorporate oceanographic and environmental conditions into fishery stock assessments. Prior to joining the FATE program, he was lead scientist for the NEFSC’s butterfish and redfish stock assessments.
Miller is also a former laboratory colleague of Kara Dodge, lead author of the leatherback tagging study that represented part of her doctoral research at the University of New Hampshire. Both Miller, then a postdoctoral researcher, and Dodge worked in the laboratory of Dodge’s advisor, Molly Lutcavage, a study co-author and scientist at the University of Massachusetts Amherst’s Large Pelagics Research Center in Gloucester, Mass.
Miller received his Ph.D. in Quantitative Ecology and Resource Management in 2005 from the University of Washington and joined the NEFSC staff in 2007. Dodge worked at the NEFSC’s Woods Hole Laboratory from 1999 to 2005 in the acoustics group, and also with the region’s marine mammal and sea turtle stranding program before she entered graduate school.
“Analyzing satellite tag data requires different statistical approaches,“ Dodge said. “The data are correlated in time and space. Traditional statistical approaches often assume these data are independent, but they are not. I needed a mixed-effects model, and Tim is an expert in this area. I asked him for guidance, and together we built a robust model that was essential to the success of our tagging study.”
“Kara thought I could help with the project, using analytical methods to understand the satellite tagging data,” Miller said, noting that he did not go to sea to tag the turtles. “I was able to provide computer code for analyses and advised her on which models to use for her specific needs. Satellite tag data are difficult to interpret. We were able to determine changes in the direction of turtle movements over time and what these meant. If the paths were straight, it implied the turtles were migrating; if the paths were not so straight, it implied the turtles were searching for food.”
In addition to Dodge, Miller and Lutcavage, the study also involved Ben Galuardi of the Large Pelagics Research Center, and Cape Cod fisherman Mark Leach of Harwichport, whose lobster boat was used to catch and tag the turtles. Spotter pilot George Purmont assisted in locating turtles. Additional collaborations with the New England Aquarium and the Provincetown Center for Coastal Studies contributed to obtaining new knowledge on leatherback health, physiology and entanglement.
Leatherbacks are the largest turtles in the world, weighing up to 2,000 pounds and can grow to be seven feet long. They eat only soft-bodied animals such as jellyfish and ctenophores, which occur in abundance during the summer and fall on the Northeast Shelf.
The researchers wanted to determine how leatherbacks behave in distinct regions, or ecoregions, of the North Atlantic based on ocean and environmental features. They also wanted to learn more about the leatherbacks diving habits, migratory patterns, and the behavior of immature or subadult and adult males. Most of what is known about leatherbacks comes from tagging studies on adult females on their tropical nesting beaches.
“We had a great team and were able to use the skills and experience of every member to make our study a success,” Dodge said of the project.
With the study complete, Dodge received her Ph.D. in 2013, and has returned to Woods Hole. She recently began a research position at the NEFSC's Woods Hole Laboratory working with turtle researcher Heather Haas of the Protected Species Branch and with collaborators from the Coonamessett Farm Foundation and the Woods Hole Oceanographic Institution. Her position is funded by the Atlantic Marine Assessment Program for Protected Species (AMAPPS). Dodge, Haas, and colleagues have several projects planned for this summer on loggerhead and leatherback turtles, using new technologies to learn more about these species, which are protected under the federal Endangered Species Act.
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